Questions on the metric units of source space

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1

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Dear MNE user,

I am trying to figure out the metric unit used in src[0]['rr'],
src[1]['rr'] and the actual brain size.
I thought the coordinate is in meter and trying to convert to cm with
the following code:

np.max(src[0]['rr'],axis=0)*100
Out[15]: array([ 0.07051213, 1.91847401, 5.94898962])
np.min(src[0]['rr'],axis=0)*100
Out[16]: array([-1.99681995, -3.02844139, 2.67239889])
np.max(src[1]['rr'],axis=0)*100
Out[17]: array([ 2.0684692 , 1.85747988, 5.92515851])
np.min(src[1]['rr'],axis=0)*100
Out[18]: array([ 0.00727971, -3.00631614, 2.51376613])

If the unit is in meter, I will get a very tiny brain.
Any suggestion on this question will be much appreciated. Thanks for your time.

Best,
Feng Liu

2

Dear Feng Liu,

units should indeed be in meters. Note that the source space is usually defined on the white matter surface, which is inside the brain and thus smaller than for example the pial surface. Is this the fsaverage or mne sample brain?

best,
Marijn.

       External Email - Use Caution

Dear MNE user,

I am trying to figure out the metric unit used in src[0]['rr'],
src[1]['rr'] and the actual brain size.
I thought the coordinate is in meter and trying to convert to cm with
the following code:

np.max(src[0]['rr'],axis=0)*100
Out[15]: array([ 0.07051213, 1.91847401, 5.94898962])
np.min(src[0]['rr'],axis=0)*100
Out[16]: array([-1.99681995, -3.02844139, 2.67239889])
np.max(src[1]['rr'],axis=0)*100
Out[17]: array([ 2.0684692 , 1.85747988, 5.92515851])
np.min(src[1]['rr'],axis=0)*100
Out[18]: array([ 0.00727971, -3.00631614, 2.51376613])

If the unit is in meter, I will get a very tiny brain.
Any suggestion on this question will be much appreciated. Thanks for your time.

Best,
Feng Liu

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3

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Dear Marijn,

Thanks a lot for your reply. I am using the sample brain automatically
downloaded from mne-python. When I checked the coordinates, I found
the range of x is about 4 cm, and the range of y is about 5 cm and the
range of z is about 3.5 cm, doesn't that look normal ?

Best,
Feng